1. Field of the Invention
The present invention relates to the field of optical couplers. In particular, the present invention relates to optical fiber coupling devices that convert a single input beam of light energy from a laser into multiple output beams of partial light energy, each of which is focused into a separate optical fiber, with improved transfer efficiency and without damage to the individual optical fibers.
2. Description of the Prior Art
Many applications for laser energy in medicine are known in the prior art. Lasers produce an intense, coherent, directional beam of light energy. Medical applications of lasers include coagulating bleeding ulcers, removing plaque (a fatty deposit) in a blood vessel, excising or vaporizing a tumor, and ablating the hard dentin or enamel of a tooth, to name a few. In order to transmit light energy needed for these surgical applications, optical fibers made of transparent materials, such as glass, fused silica or the like, are utilized to channel and direct the energy. Either a single discrete fiber or a bundle of fibers may be used to transmit the light energy.
A relatively large diameter optical fiber, such as one with a core diameter of 1,000 microns, can transmit a relatively great amount of light energy without damage to the integrity of the optical fiber. However, where flexibility is needed, for example, to enable the optical fiber to pass through a tortuous blood vessel or to reach a relatively inaccessible site in a body behind other structures, a single, relatively large diameter optical fiber may not be sufficiently flexible. While a relatively smaller diameter optical fiber, such as one with core diameter of 50 or 100 microns, may provide more flexibility, a small diameter optical fiber is often unable to carry a sufficiently large amount of light energy without significant damage to the optical fiber.
To transmit large amounts of light energy, while retaining needed flexibility, it is frequently necessary to use a plurality of smaller diameter optical fibers in a bundle, thereby dividing the light energy into several parts so that the energy carried by each individual optical fiber is not excessive. The use of multiple optical fibers, each carrying a portion of the light energy needed to accomplish the desired result, is particularly advantageous, for example, in the transmission of extremely high intensity pulsed light energy from a xenon chloride (excimer) laser at a wavelength of 0.308 microns through quartz or fused silica optical fibers with a high hydroxyl content, or from a holmium:YAG laser at a wavelength of 2.1 microns, through quartz or fused silica optical fibers with a low hydroxyl content. It would be desirable to transmit light energy from an erbium:YAG laser at a wavelength of 2.94 microns. However, light energy of this wavelength cannot be efficiently transmitted through conventional quartz or fused silica fibers. Zirconium fluoride fibers, the fibers of choice for that purpose, can transmit only a small amount of said light energy without fracturing or melting and-releasing toxic gas.
In delivering light energy from a laser to a bundle of fibers, there are significant losses of light energy. This is part of the problem that the present invention addresses. Primarily, the energy losses occur because the emitted laser beam is focused on a cross section of fibers in the bundle, and a portion of the light energy is lost in the spaces between the fibers as well as in the cladding which surrounds each fiber. Furthermore, where the laser emission is in a gaussian pattern, the fibers in the center of the bundle receive a larger amount of light energy than those in the periphery of the bundle.
Since many applications require the delivery 10 of more light energy than one optical fiber of relatively small diameter can effectively and safely transmit, it would be useful to have a device which could divide the light energy from a single laser source into a plurality of relatively equal individual beams, with each beam independently directed toward an individual focal point, so that the proximal end faces of a corresponding plurality of individual optical fibers could each be positioned at one of the focal points. Since each optical fiber would be individually positioned to receive a proportionate amount of the light energy from the partitioned beam, the device would avoid the substantial losses of light energy associated with the coupling inefficiencies in the past. In addition, since the method of light beam partitioning would divide the light energy into relatively equal, separate parts, below the damage threshold of the receiving optical fiber, each of the individual fibers in the bundle could receive and transmit an equal amount of laser light energy without damage thereto.
However, the division of laser light energy into the individual fibers in the bundle does not necessarily need to be equally distributed; nor does the predominant spectral line that is delivered to each individual fiber need to be the same wavelength. Also, by focusing the light energy delivered to each individual optical fiber, the light energy could be delivered to each individual optical fiber with a spot size area and convergence angle which is most suitable for entry into that optical fiber.
Therefore, there is a need for a light energy coupling device and method to divide light energy from a single transmission path into a plurality of transmission paths; where the plurality of individual transmission paths are directed toward and focused into a corresponding plurality of individual optical fibers; and, where the light energy directed into each optical fiber does not exceed its damage threshold. The present invention satisfies the foregoing needs.
The following patents describe light energy coupling devices and methods.
U.S. Pat. No. 4,933,949, to Johnson (hereafter the "Johnson Patent") for "Arrangement for Multiplexing and Intensity Splitting Light Beams for Interface into Fiber Optic Cables".
U.S. Pat. No. 4,961,622, to Gorman et al. (hereafter the "Gorman Patent") for "Optical Coupler and Refractive Lamp".
U.S. Pat. No. 4,868,361, to Chande et al. (hereafter the "Chande Patent") for "Coupling Device for High Power Laser Beam Transmitting Optical Fibers".
U.S. Pat. No. 4,917,084, to Sinofsky (hereafter the "First Sinofsky Patent") for "Infrared Laser Catheter System".
U.S. Pat. No. 4,950,266, to Sinofsky (hereafter the "Second Sinofsky Patent") for "Infrared Laser Catheter System".
U.S. Pat. No. 4,925,265, to Rink et al. (hereafter the "Rink Patent") for "Apparatus for Directing a Laser Beam into Optical Fibers".
The Johnson patent discloses an optical mixing bar of sufficient length to permit mixing of light therein. The mixing bar has a plurality of facets on the beam input end. There are means for directing separate laser beams into each of the facets of the mixing bar. The light energy mixes within the mixing bar and the output of the mixing bar is a single beam of laser light energy approximately equal to the sum of the energies of the input beams. In the present invention, there is a single light energy beam at the input, and that beam is permitted to pass through an optical system that separates the light into a plurality of separate open or free beam paths that converge at a plurality of associated focal regions. In contrast, the Johnson patent teaches to combine a plurality of mixed input beams into plural output beams, a different purpose than that contemplated by the present invention. In addition, the present invention permits fine mechanical positioning of the multiple output beams to enhance their alignment into the individual optical fibers.
The Gorman Patent discloses an optical coupler and refractive lamp. The Gorman Patent describes an optical system that produces an input ring of laser light energy. A plurality of optical fibers are arranged concentrically in a ring opposite the ring of laser light energy. The present invention is an improvement over the Gorman Patent, because the present invention focuses a portion of the input energy precisely into each of a plurality of individual optical fibers, thereby increasing the transmission efficiency.
The Chande patent discloses an optical system for coupling a high power laser beam from one optical fiber into another optical fiber. There is a mounting means, so that both the input optical fiber and the output optical fiber can be retained in alignment. The Chande patent is different from the present invention, in that the present invention transmits the input light energy from a single source into a plurality of output optical fibers. In contrast, the light energy coupling in the Chande patent is limited to transmitting light energy from a single input fiber into another single output fiber.
The Sinofsky patents disclose an infrared laser catheter system which is utilized for the percutaneous removal of atherosclerotic plaque. A single beam of light energy is directed toward the proximal ends of several optical fibers. In the four-fiber coupling system of the Second Sinefsky patent, a portion of the laser light is transmitted into four mirrors, each of which reflects the laser light into one of four lenses, that each focus the light energy into one of four optical fibers that are retained in four fiber optic connectors. In contrast, in the present invention, the beam is partitioned and individually directed into a plurality of optical fibers. The present invention utilizes fewer optics than the Sinofsky invention. Also, it is not necessary for the single input beam of the present invention to be divided by mirrors or beam splitters, as taught by the Sinofsky patents. In addition, the present invention provides increased coupling efficiency.
The Rink patent discloses an apparatus for directing a laser beam into optical fibers. The apparatus utilizes a movable lens which steers the beam serially into individual optical fibers. In contrast, the present invention utilizes optics in a fixed position, the output of which is focused into individual optical fibers. The present invention differs from the Rink patent, in that a single path of light energy in the present invention is simultaneously divided and focused into a plurality of open or free beam paths without moving parts.
None of the aforementioned prior art has implemented an optical coupling device and method where the light energy is transferred from a single source and along a single transmission path into a plurality of open or free beam transmission paths by a partitioning optical system, where the plurality of transmission paths are directed toward and focused into a corresponding plurality of optical fibers, and where the energy directed into each optical fiber does not exceed its damage threshold; all in a manner that improves the transfer efficiency of the optical coupling without moving parts.